The present invention relates to a two-way insert valve which has the features set forth in the preamble to Claim 1.
The term "two-way insert valve" is the additional designation for a hydraulic control element according to DIN 24 342. It is also known by the name of logic element or cartridge. In its basic principle, there is concerned a 2/2-way valve and therefore a directional control valve having two working connections and the two switch positions, open and closed. It is therefore designed to be installed in a receiving bore hole in a control block. By suitable control and connection of two-way insert valves, the direction of flow and the size as well as pressure of a stream of liquid can be controlled. The valve can therefore assume directional functions, flow functions, or pressure functions. The technique of the two-way insert valves is described in detail in the bock "Der Hydraulik-Trainer" The Hydraulic Trainer!, Vol. 4, 1st Edition, published by Mannesmann Rexroth GmbH in 1989.
A two-way insert valve consists essentially of an insert assembly which can be installed in the receiving bore hole of the control block and of a valve cover which closes the receiving bore hole. The insert assembly, on its part, comprises a bush-like housing which is arranged fixed in position in the control block and has a plurality of radial passages and an axial passage as well as a valve piston which is displaceable axially in the housing and by which a connection between the radial passages and the axial passage can be controlled and which can be displaced as far as a stop in the open direction. Normally, the insert assembly also includes a closure spring which acts on the valve piston. The bush-like housing can be formed in one piece by a single bush, as is true of the two-way insert valves shown in said book, or of a two-way insert valve known from EP 0 634 577 A1.
In other embodiments, the housing is made in two parts and has a bush in which the radial and axial passages lying in the main stream are located and a ring arranged between the bush and the valve cover. In accordance with the preamble to Claim 1, the invention relates to such a two-way insert valve.
Such a two-way insert valve is already known, for instance, from "RD-Blatt" 81 056/4.79 of Mannesmann Rexroth GmbH, or from the brochure HP/VEK 2-AKY 011/1 Ger/Eng/Fr (5.90) of Robert Bosch GmbH. In both of the previously known two-way insert valves of the bipartite construction, the valve piston is guided axially in the bush and strikes against the ring upon the maximum stroke. In the two-way insert valve in accordance with the "RD-Blatt", the guidance length between the bush and the valve piston is independent of the position at the time of the valve piston and corresponds approximately to the distance of the first end of the bush facing the ring from the radial passages, less the maximum stroke of the valve piston. This follows from an external milling on the valve piston, which milling is in the region of the radial passages in the closed position of the valve piston.
In the two-way insert valve of the Bosch prospectus, the guidance surface on the valve piston extends, in the closed position of the piston, by approximately a distance corresponding to the maximum stroke, into the region of the radial passages of the bush. This has the result that, upon an increase in the stroke of the valve piston, the guidance length is increased and corresponds approximately to the distance of the end of the bush facing the ring from the radial passages when the valve piston is against the ring.
A given nominal size being presupposed, it is endeavored to develop a two-way insert valve that the pressure drop occurring upon the flow of a large amount of pressurized fluid through the valve is very slight.